The influence of carbohydrate ingestion on peripheral and central fatigue during exercise in hypoxia: A narrative review

A Review of Carbohydrate Supplementation Approaches and Strategies for Optimizing Performance in Elite Long-Distance Endurance

Carbohydrate supplementation is a common practice among endurance athletes participating in long-distance competitions. However, glycogen storage regulation, in-competition blood glucose levels, and their relationship with athletic performance are influenced by multiple factors. This review summarizes the recent research progress on carbohydrate supplementation, addressing its applications in the pre-, during-, and post-competition phases. It explores variables that influence the effectiveness of carbohydrate supplementation and provides a summary of strategies, based on six key aspects: carbohydrate properties, multi-nutrient interactions, gastrointestinal function, individual differences (such as age and gender), environmental conditions, and psychological factors. The combination of different types, ratios, and concentrations of carbohydrates has been demonstrated to enhance the efficiency of carbohydrate digestion and absorption. The synergistic combination of protein, sodium, and caffeine intake demonstrates enhanced efficacy in carbohydrate supplementation strategies. Gastrointestinal tolerance training for carbohydrate supplementation has been identified as an effective measure to alleviate gastrointestinal discomfort during high-dose carbohydrate intake. The adjustment of the carbohydrate-to-fat ratio and the type of carbohydrate intake has been found to mitigate the impact of gender and menstrual cycles on glycogen storage and substrate utilization. Modifying the timing of glycogen storage and regulating the concentration and temperature of carbohydrate solutions during competition have been demonstrated to facilitate coping with the elevated energy expenditure and metabolic substrate shift from fat to carbohydrates, triggered by a combination of environmental and psychological factors, including special environmental and climatic conditions (e.g., high altitude, high temperature, high humidity, and cold) and emotional states (e.g., pre-competition stress and anxiety during the competition). To achieve precise carbohydrate supplementation for athletes in major events under various competitive environments, it is necessary to quantitatively assess the effects of carbohydrate supplementation, supported by mechanistic studies. This can be achieved by utilizing wearable devices to monitor the entire competition, coupled with data collection technologies, such as high-throughput profiling. Furthermore, emerging data analytics techniques, such as machine learning and causal inference, should be leveraged to refine supplementation strategies.

The effect of carbohydrates with different levels of digestibility on energy metabolism in vivo under hypobaric hypoxic conditions

Current strategies for improving energy supply in hypobaric hypoxic environments are limited. Therefore, this study investigates the effects of four carbohydrates with different levels of digestibility on energy metabolism in vivo in hypobaric hypoxic environments. First, we characterized the four types of carbohydrates. Subsequently, reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to characterize the expression of GLUT1, GLUT2, and SGLT1 in the glucose transport pathway in vivo. In addition, the effects of different levels of carbohydrate digestibility on energy expenditure were evaluated in vivo. The results showed that pre-gelatinized corn starch significantly increased GLUT1 gene expression in the hypobaric hypoxic conditions (1.58 times, compared to normobaric normoxic). In addition, pre-gelatinized corn starch increased energy expenditure in the hypobaric hypoxic conditions and performed better in terms of glycogen accumulation and glucose transport. Therefore, pre-gelatinized corn starch administration may be a promising strategy for long-term energy supplementation in hypobaric hypoxic.

Ginsenosides, salidroside, and syringin complex exhibits anti-fatigue in exhaustive exercise rats

Excessive exercise can lead to fatigue, consequently affect exercise performance, and further have an adverse impact to human health. The synergistic effects of ginsenosides, salidroside, and syringin on improving exercise performance remain unknown. Hence, the effects of Chinese herb powder (CHP) which consisted of bioactive compounds such as ginsenosides (Rg1, Re, and Rb1), salidroside, and syringin on exercise performance, energy metabolism, tissue damage, antioxidant activity, and inflammatory cytokine were investigated in exhaustive exercise rats. Male Sprague-Dawley rats aged of 8-week-old were randomly assigned into four groups: control (normal, N), low-dose (L, 310 mg/kg bw), medium-dose (M, 620 mg/kg bw), and high-dose (H, 1550 mg/kg bw) groups. The intervention groups were orally given CHP daily for successive 30 days. Abdominal arterial blood, liver, and gastrocnemius muscles were collected 4 hours after exhaustive exercise for further analysis. The high-dose CHP group increased the time to exhaustion, decreased serum lactate level, increased serum superoxide dismutase activity, and decreased liver interleukin-6 concentration. Therefore, CHP exhibits an anti-fatigue effect for prolonging the time to exhaustion through improving lactate clearance, and to a lesser extent, enhancing the capacity of antioxidation and anti-inflammation.

Improving Endurance Exercise Performance at High Altitude: Traditional and Nontraditional Approaches

Acute exposure to terrestrial altitude (hypobaric hypoxia) causes decrements in endurance performance relative to sea level. Altitude acclimatization consistently results in partial attenuation of these decrements, but due to logistical challenges, it is not readily implemented. We discuss mechanisms and impact (or lack thereof) of other non-acclimatization interventions to improve endurance performance and provide suggestions for future research directions.

Exercise-Induced Central Fatigue: Biomarkers, and Non-Medicinal Interventions

Fatigue, commonly experienced in daily life, is a feeling of extreme tiredness, shortage or lack of energy, exhaustion, and difficulty in performing voluntary tasks. Central fatigue, defined as a progressive failure to voluntarily activate the muscle, is typically linked to moderate- or light-intensity exercise. However, in some instances, high-intensity exercise can also trigger the onset of central fatigue. Exercise-induced central fatigue often precedes the decline in physical performance in well-trained athletes. This leads to a reduction in nerve impulses, decreased neuronal excitability, and an imbalance in brain homeostasis, all of which can adversely impact an athlete's performance and the longevity of their sports career. Therefore, implementing strategies to delay the onset of exercise-induced central fatigue is vital for enhancing athletic performance and safeguarding athletes from the debilitating effects of fatigue. In this review, we discuss the structural basis, measurement methods, and biomarkers of exercise-induced central fatigue. Furthermore, we propose non-pharmacological interventions to mitigate its effects, which can potentially foster improvements in athletes' performances in a healthful and sustainable manner.

Meta-Analysis of Carbohydrate Solution Intake during Prolonged Exercise in Adults: From the Last 45+ Years' Perspective

Carbohydrate (CHO) supplementation during prolonged exercise postpones fatigue. However, the optimum administration timing, dosage, type of CHO intake, and possible interaction of the ergogenic effect with athletes' cardiorespiratory fitness (CRF) are not clear. Ninety-six studies (from relevant databases based on predefined eligibility criteria) were selected for meta-analysis to investigate the acute effect of ≤20% CHO solutions on prolonged exercise performance. The between-subject standardized mean difference [SMD = ([mean post-value treatment group-mean post-value control group]/pooled variance)] was assessed. Overall, SMD [95% CI] of 0.43 [0.35, 0.51] was significant (p < 0.001). Subgroup analysis showed that SMD was reduced as the subjects' CRF level increased, with a 6-8% CHO solution composed of GL:FRU improving performance (exercise: 1-4 h); administration during the event led to a superior performance compared to administration before the exercise, with a 6-8% single-source CHO solution increasing performance in intermittent and 'stop and start' sports and an ~6% CHO solution appearing beneficial for 45-60 min exercises, but there were no significant differences between subjects' gender and age groups, varied CHO concentrations, doses, or types in the effect measurement. The evidence found was sound enough to support the hypothesis that CHO solutions, when ingested during endurance exercise, have ergogenic action and a possible crossover interaction with the subject's CRF.